The present invention relates to water heater devices and more particularly to a thermally insulated water heater device construction, and a method of manufacturing a thermally insulate water heater device.
Typically, water heaters are formed of an inner water tank with an outer shell located over the inner tank with an annular space therebetween. The space between the inner tank and outer shell is filled with a thermal insulation. For many years fiber glass has been used as the insulation material between the inner tank and outer shell. More recently, a foam such as urethane, has been used as the thermal insulation material in place of fiber glass between the inner tank and outer shell. Typically, a foamable material is injected into the space between the inner tank and outer shell, and is allowed to foam in situ. However, there is a problem in restraining the expanding foam within the annual space and more particularly within a predetermined location or region within the annular space. This is especially important when using foam insulation in a gas-fired type water heater wherein it is extremely undesirable to have flammable foam in proximity to the gas burner of the water heater.
Various proposals have been made to solve this problem. U.S. Pat. No. 4,372,028 issued on Feb. 8, 1983 shows water heater having a foam filled closed collar located in the annular space between the inner tank and outer shell at the bottom of the inner tank, and the annular space above the collar filled with expanded foam. The collar functions as a stop to the expanded foam in the annular space thereabove. This patent further shows a method of manufacturing the water heater which includes the steps of forming a flexible, expandable closed elongated bag having a hole therein through which an expandable foam can be injected into the bag. The bag is filled with a foam material which expands the bag to form a collar, and before the foam material has had sufficient time to fully expand, the bag opening is sealed and the bag is circumferentially wrapped around the lower end of the tank with the bag ends overlapping each other. Next, before the foam material in the collar has had sufficient time to expand, the outer shell is positioned over the inner tank and bag. The foam in the bag expands forming a collar which is in compression between the inner tank and outer shell. The annular space above the collar is then filled with expandable foam material.
U.S. Pat. No. 4,447,377 issued on May 8, 1977 shows a gas fired water heater wherein a layer of fiberglass insulation material is wrapped around the bottom portion of the inner water tank around the combustion chamber and a plastic envelope is wrapped around the inner tank above the fiberglass insulation. The envelope is in the form of an elongated thin tube having an inner wall, an outer wall, a bottom wall, two end walls and an open top. When wrapped around the inner tank, the end walls of the envelope abut each other. The outer shell is positioned over the inner tank such that the envelope is in the annular space therebetween. Expandable foam is injected through the open envelope top into the envelope and allowed to expand therein.
U.S. Pat. No. 4,477,399 issued on Oct. 16, 1984 shows a water heater having an inflatable toroidally shaped tube located around the bottom end of the inner tank such that when the toroidal tube is inflated with air, it seals the bottom end of the annular space between the inner tank and outer shell. A foamable material is then injected into the annular space above the toroidal tube to fill the annular space.